Effect of Hydrophilic Additives on the Rheological Properties of the Finely Dispersed Part of Magnetite Concentrate

I. N. Lantsman, E. N. Chulkova, V. M. Vitrugin

(Submitted by the scientific seminar of the Department of OKhT)

As is known, the introduction of hydrophilic additives into fine-grained iron-ore concentrates ensures the stability and efficiency of the pelletizing process [1]. A substantial influence on the pelletizing process is exerted by the finest-dispersed, so-called slime fraction with a particle size of 30–0 μm. For a deeper study of the mechanism of action of hydrophilic additives, investigations were carried out of the rheological properties of the slime fraction of magnetite concentrate from the Sokolovsko-Sarbaiskii mining and processing combine and of mixtures based on it. As additives, the pink variety of Taganskii bentonite and the coal-alkali reagent UShR from the Karaganda plant “Utyazhelitel” were used. The investigations were carried out on an RV-8 rotational viscometer. Taking the working moisture content of the pelletized mass to be within 8–10% and assuming that the finely dispersed fraction and water form a porous suspension inside the pellet being formed, suspensions in the concentration range 20–57% were prepared for study. The content of the slime fraction in the concentrate was 1.5%. The rheological properties of the mixtures were studied with bentonite additions of 1–2% and UShR additions of 0.1–0.7%, calculated with respect to the dry mass of the concentrate. To determine the mechanism of action of these additives, more concentrated systems were also studied: slime–water and UShR–water.

Table 1

Rheological properties of slime suspensions

The results of studies of slime suspensions, given in Table 1, show that at comparatively low concentrations (up to 15%) the suspension is a weakly structured, weak system. With an increase in concentration to 57%, along with the growth of the yield shear stress ($\theta$) and plastic viscosity ($\eta_{\mathrm{pl.}}$), the plasticity ($\psi$) also increases. Slight structuring leads to a decrease in relative plasticity ($\psi'_{\mathrm{rel.}}$). In the concentration range of 15–30%, encountered under practical conditions, the slime suspension cannot provide the plastic deformations necessary for granule formation.

Table 2

Rheological characteristics of Tagan pink bentonite

The rheological properties of suspensions of Tagan bentonite of the pink variety are presented in Table 2. With increasing bentonite concentration, the yield stress and plastic viscosity increase. The maximum plasticity is attained at $c = 16\%$. At this same concentration the maximum relative plasticity is also observed. The values of the relative plasticity of bentonite suspensions are an order of magnitude higher than those of slime suspensions.

Comparison of the rheological characteristics of the sludge–bentonite–water system (Table 3) with the bentonite–water (Table 2) and sludge–water (Table 1) systems shows that mixing suspensions of sludge and bentonite leads to mutual coagulation and, as a consequence, to a decrease in the number of particles and a sharp reduction in plastic viscosity.

An increase in the concentration of solid in the system as a whole leads to an increase in the limiting shear stress and plastic viscosity. Pore suspensions consisting of sludge and bentonite particles reach a maximum of plasticity at lower concentrations of the solid phase than do pure sludge suspensions.

From the values of relative plasticity it may be concluded that, in such a system, the plastic deformations necessary for granule formation are sufficiently developed. At the same time, the maximum value of relative plasticity with the addition of bentonite increases as a result of a sharp increase in the efficiency of coagulation structure formation.

Table 3

Rheological properties of pore suspensions of charges

The change in the rheological properties of the carbon-alkaline reagent–water system in the concentration range of 3–40% is shown in Table 4.

With increasing concentration of CAR, the shear stress increases, although the absolute values of \(\theta\) are small. However, with increasing concentration of CAR the plastic viscosity increases sharply. This is associated

because the larger humate molecules, being distributed throughout the volume of the system, have a high adsorption capacity.

Table 4

Rheological properties of UShR solutions

Table 5

Effect of UShR on the rheological properties of rock suspensions

The addition of UShR to the clay of magnetite concentrate in the ratio clay:water:UShR = 22 : 24.5 : 1.46 (Table 5) stabilizes the system; therefore, at identical shear stresses the viscosity value decreases somewhat. Further addition of UShR leads to weak structuring with a slight increase in viscosity. Increasing the UShR concentration to 0.7% leads to a sharp increase in viscosity, which indicates structuring of UShR throughout the volume. The maximum plasticity occurs with the addition of 0.4% UShR at a suspension concentration of 47.3%.

Thus, by introducing bentonite into the lumped charge, an increase in the concentration of the rock suspension is achieved at the expense of the plastic material, which promotes the formation of a stronger structure possessing the plasticity required for granulation.

The carbohydrate reagent increases the plasticity of the mass as a result of modification and hydrophilization of the magnetite surface, which leads to the creation of a strong and readily recoverable structure.

Consequently, the role of the added hydrophilic components is reduced to the creation of labile, readily recoverable, minimally strong structures that facilitate the formation and compaction of granules as they move along the plane of the granulator.